Mitigate presumed OOM in CircleCI (#11206)

Summary:
We've seen many instances of
build-linux-static_lib-alt_namespace-status_checked failing like this:
```
g++: fatal error: Killed signal terminated program cc1plus
compilation terminated.
make: *** [Makefile:2507: utilities/transactions/transaction_test.o]
Error 1
```

It's understandable that so many static linking jobs could exhaust memory.

The executor only has 16 vcores, so going from 32 down to 24 shouldn't hurt build time.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/11206

Test Plan: will watch CI

Reviewed By: ajkr

Differential Revision: D43137246

Pulled By: pdillinger

fbshipit-source-id: 050b0f700c285dd913bcae8b4a76a44d04bb0356

.circleci/config.yml

@@ -278,7 +278,7 @@ jobs:
     resource_class: 2xlarge
     steps:
       - pre-steps
-      - run: ASSERT_STATUS_CHECKED=1 TEST_UINT128_COMPAT=1 ROCKSDB_MODIFY_NPHASH=1 LIB_MODE=static OPT="-DROCKSDB_NAMESPACE=alternative_rocksdb_ns" make V=1 -j32 check
+      - run: ASSERT_STATUS_CHECKED=1 TEST_UINT128_COMPAT=1 ROCKSDB_MODIFY_NPHASH=1 LIB_MODE=static OPT="-DROCKSDB_NAMESPACE=alternative_rocksdb_ns" make V=1 -j24 check
       - post-steps
 
   build-linux-release: